Write to multiple IOs in linear fashion

[Vincent Marquez]

I have a common use case where my pipeline looks like this:
CassandraIO.readAll -> Aggregate -> CassandraIO.write -> PubSubIO.write

I do NOT want my pipeline to look like the following:

CassandraIO.readAll -> Aggregate -> CassandraIO.write
                                                         |
                                                          -> PubsubIO.write

Because I need to ensure that only items written to Pubsub have
successfully finished a (quorum) write.

Since CassandraIO.write is a PTransform<A, PDone> I can't actually use it
here so I often roll my own 'writer', but maybe there is a recommended way
of doing this?

Thanks in advance for any help.

*~Vincent*